£42 - see here:
http://www.caa.co.uk/docs/175/New%20...icences_v3.pdf
It's the same process as asking them to verify your licence for the issue of a foreign licence. But, you need to be a company, NAA or airline to do it, by the look of it. I'd give them a ring.
If you are just nosey about someone's qualifications I doubt they would play ball. Though if you suspect someone of flying without a licence I'm sure they would look into it...
Tim